RO desalination systems are well known in the art. With reference to FIG. 1, an example of an RO desalination system is shown:
The RO desalination system of the kind described above generally designated at 1 comprises a plurality of pressure vessels (PVs) 2 held by a support construction 3, the construction 3 comprising holders 4 for supporting each of the PVs 2 in a horizontal orientation. Each of the PVs is in fact suspended by the support construction 3 so that it is supported from underneath at several points along its length.
Each PV 2 has front and rear ends and has a centrally disposed permeate tube connected to a front product line 5 at the front end of the PV and to a rear product line (not seen) at the rear end of the PV. Each PV 2 is further connected at its front end to a feed line 6 for supplying to the PC raw fluid to be desalinated, and at its rear end to a brine (brine) line (not seen).
Each of the PVs 2 has a plurality of RO membranes 10 mounted therein, whose typical design is shown in FIG. 2. As seen in FIG. 2, the membrane 10 comprises a perforated permeate tube 12 with a multi-layer membrane sheet 14 wound thereon constituting a membrane core, and an encapsulating outer shell 18.
The wound multi-layer membrane sheet 14 defines a reject side on one surface thereof, coming in contact with the feed water, and a permeate side, on the opposite surface thereof, coming in contact with feed water which has passed through the sheet by reverse osmosis, i.e. permeate. The permeate tube 12 is formed with holes 13 adapted for collecting said permeate, which is adapted for withdrawal from the PV via its front and rear central ports 12a and 12b constituted respectively, by front and rear ends of the permeate tube 12 of the membrane 10.
The multi-layer membrane sheet 14 comprises two membrane layers 14a, a permeate layer 14b positioned therebetween, and a feed spacer 16. The multi-layer membrane sheet 14 is wound on the permeate tube 12, its front end 12a being adapted for fluid communication with the feed line 6, constituting thereby a circumferential, feed inlet port 17a of the PV for conducting raw fluid to be desalinated thereto, and its rear end 12b being adapted for fluid communication with the brine line, constituting thereby a circumferential, brine outlet port 17b of the PV for the withdrawal of the brine therefrom.
In operation, feed water F is provided to the circumferential, feed inlet port 17a at the front end 12a of the PV, to flow axially in the direction of arrows 19. Permeate P is collected by the permeate tube 12 to exit through the front and rear central ports 15a, 15b, respectively, and brine (sometimes referred to as ‘concentrate’) B is removed through the circumferential outlet port 17b at the rear end 12b of the PV.
In assembly, the membrane 10 is located within the PV 2 such that the front and rear permeate ports 15a, 15b are connected to the front and rear permeate lines 5 respectively, the front circumferential port 17a is connected to the feed line 6, and the rear circumferential port 17b is connected to the brine line.
When loading a membrane 10 into the PV 2, the membrane 10 is inserted into the PV 2 horizontally, and is displaced within the PV 2 until it reaches its desired location therein. When unloading a membrane 10, both ends of the PV 2 are opened, whereby the membrane 10 may be pushed from one side of the PV 2 to exit from the other side thereof.
However, there have been known designs in which PVs are disposed vertically, i.e. the PV having a top end and a bottom end, and wherein loading and unloading of membranes was performed through the top end of the PV. Since loading and unloading of membranes is a generally complicated and time consuming process, such PVs are known to employ a small number of membranes, e.g. one or two, and of smaller diameter (and thus of correspondingly smaller weight).